This invention relates to peptide-based compounds having light-emitting moieties. Peptides may be chemically linked with detectable “labels” and used as probes, for example, to monitor peptide, cytokine, drug, and hormone receptors at the cellular level. Typically, the labeled peptide is placed in contact with a tissue or cell culture where it binds to an available receptor. Once bound, the label is detected, allowing properties such as receptor distribution or receptor binding kinetics to be monitored.
Peptides are typically labeled with radioactive elements such as 125I or 3H. In this case, emission of high-energy radioactive particles is monitored using standard γ-ray detectors, thereby allowing detection of the label. While detection techniques for 125I and 3H are well-known, radioactive compounds by nature have limited half lives, and are often both toxic and expensive. Moreover, current detection technology makes it difficult or impossible to detect radioactive probes in real-time, thereby precluding study of kinetic processes.
Bombesins are a family of peptide neurotransmitters that share a common C-terminal amino acid sequence Trp-Ala-X-Gly-His-X-Met-NH2. Bombesin-like peptides include gastrin releasing protein (GRP) neuromedin B (NMB), neuromedin C (NMC), ranatensin, litorin and phyllolitorin. Bombesin-like peptides are particularly desirable peptides to label and use to monitor cell receptors, as these peptides exhibit multiple biological roles and their receptors are located in a variety of tissues. Specifically, bombesin-like peptides are localized to the brain (being particularly associated with neurons), intestine, lung, adrenal gland, and pituitary. Receptors for bombesin-like peptides include, for example, bombesin 1 receptor (BB1 or NMB receptor), the bombesin 2 receptor (BB2 or GRP receptor), and bombesin 3 receptor (BB3 or orphan bombesin receptor) and the NMB receptor. Binding to a cognate receptor by a bombesin-like peptide stimulates neurotransmitter activity, (e.g., influencing thermoregulation, homeostasis, metabolism, behavior, stimulation of smooth muscle contraction (e.g., of the intestine, uterus, bladder, etc.), and glandular secretion (e.g., pancreas, anterior pituitary, etc.). Peripheral receptor binding is associated with mitogenic activity in lung cells, (including small-cell lung carcinomas), gastrointestinal tract.
There exists the need for peptides that are chemically linked with detectable labels that are easily detected, yet do not decrease the biological activity of the peptide.